The present invention relates to an apparatus for mixing a gas and a liquid at a downhole location and more particularly relates to an inexpensive mixing apparatus for saturating a liquid with a gas at a downhole location wherein the mixing apparatus can easily be run into and out of a well.
In producing minerals from a subterranean formation, there are instances where the formation requires treatment with a gas-saturated liquid. For example, in a typical in situ leach operation, wells are completed into a leachable, mineral-bearing formation, and a leach solution is flowed between wells to dissolve the mineral values into the leach solution. The pregnant leach solution is produced to the surface where it is treated to recover the mineral values from the leach solution.
Many leachable mineral values, as they occur in their natural state in a formation, must be oxidized to a higher valence before they become soluble into a leach solution. For example, uranium is normally present in a formation in the tetravalent state and must be oxidized to the hexavalent state to render it soluble in a suitable leach solution, e.g., an aqueous carbonate solution. To oxidize uranium to its higher valence, it is customary to contact the uranium in the formation with an oxidant which may be injected directly into the deposit or which may be mixed into the leach solution and injected therewith.
Several oxidants have been proposed for this purpose, including gaseous oxidants such as air and oxygen. For example, in U.S. Pat. No. 3,708,206, oxygen is injected into a formation prior to or simultaneously with a leach solution. In U.S. Pat. No. 3,713,698, air is injected through a production well to oxidize uranium values prior to injecting a leach solution through an injection well. In both U.S. Pat. Nos. 3,640,579 and 3,860,289, oxygen is supplied through a tube to a downhole location where it is bubbled into a leach solution before the leach solution is injected into a formation.
With each of these types of injection schemes, excess quantities of oxygen are required to dissolve a sufficient amount of oxygen into the leach solution. For example, where oxygen is merely bubbled into the leach solution downhole before the leach solution enters the formation, experimentation suggests that a tenfold to fifty-fold excess of oxygen over the saturation requirement is needed to bring the leach solution to a level of 80% oxygen saturation, resulting in excessive oxygen costs.
Therefore, it has been proposed to mix the gas such as oxygen and liquid such as leach solution at a downhole location in such a manner that the liquid is substantially fully saturated with little or no excess gas being required. Methods and apparatuses for mixing gas and liquid at a downhole location in this manner are fully disclosed in copending U.S. applications Ser. Nos. 846,863 and 846,874, both filed Oct. 31, 1977. While the apparatuses disclosed in these copending applications perform satisfactorily to accomplish their tasks, both are relatively expensive to construct and relatively difficult to install.